Temperature dependence of swift heavy ion irradiation induced hillocks in TiO2

Abstract

Irradiation temperature dependant morphology of near surface latent tracks and surface hillocks in TiO2 was investigated. Irradiation was performed on single crystal [110] oriented rutile using 220 MeV Xe ions to a fluence of 5 × 1010 ions cm−2. Irradiations were performed at 80 K, 300 K, 600 K, 800 K and 1000 K. It was found that average hillock height increased with irradiation temperature although large specimen-to-specimen and hillock-to-hillock size differences were also recorded. Similarly the low density conical zone in the near-surface region of the ion track increased in both length and continuity with increasing temperature. At lower temperatures this zone was found to consist of closely spaced low density pockets that become more densely arranged and almost continuous at 1000 K. Evidence supporting the idea that surface hillocks are due to expelled matter from the track core was found in that larger hillocks are subtended by larger conical zones. These experimental observations were discussed in the framework of a simple model based on the inelastic thermal spike (i-TS) model as well as Bernoulli’s principle which could satisfactorily recreate the observed trends in hillock height and further supports the idea of expelled matter forming hillocks. Strain contrast around latent tracks is mostly absent around the conical zones suggesting some relaxation due to matter expulsion. All hillocks were found to be crystalline and epitaxial with the original crystal surface.